Gas tube assembling method



April 3, 1956 P. E. GATES GAS TUBE. ASSEMBLING METHOD 2 Sheets-$heet 1 Filed July 17, 1951 PRIOR ART L vi.

IIIII m: ,5? Iiii INVENTOR PAUL 5.64m;

ATTORNEY April 3, 1956 E, GATES 2,740,186

GAS TUBE ASSEMBLING METHOD Filed July 17, 195] 2 Sheets-Sheet 2 llll PAUL E. GATES %J5)4% ATTORNEY United @tates 2,740,186 GAS TUBE sssnrtntnsannzrnon Application July '17, 1951, Serial No. 237,258 1 Claim. (Cl. 29-4513) The present invention relates to assemblies of electrodes in gas filled electric discharge tubes used in microwave systems, and to methods of making such assemblies.

This invention will be understood from its application to a particular type of gaseous discharge device described in detail below, as a matter of convenience, but variations of the particular configurations and applications to other types of tubes will be readily apparent to those skilled in the art. In these tubes, it is currently required that a glow discharge be established between two electrodes, Where the volume of ionized gas and the intensity of the ionization must be accurately controlled and should be as nearly alike as possible from each tube to the next. Transmitter-receiver (TR) and attenuator tubes as well as some forms of anti-transmit-receiver (ATR) tubes are types of gaseous discharge tubes in which the problem arises. In these tubes, a Waveguide passage is often defined by a metal portion of the tube envelope. The ionizationcontrols the transmission of microwave energy in this transmission path. In the case of TR and ATR tubes, the ionization that is to be established as a weakly ionized discharge between the electrodes in question, is to facilitate the intense ionized discharge or break-down across the transmission path when high level microwave energy is impressed on the device.

Certain forms of these tubes have heretofore included a glass sheathed wire or rod, extending concentrically within a hollow cone to an opening at the end of the cone, where both the inner electrode and the cone are exposed to the gas filling within the transmission path. By applying a voltage of suitable magnitude between this inner electrode and the cone, a gaseous electric discharge is established.

In order that the control may be effected uniformly from each tube to the next, it has been found critically important that the concentricity of the inner. electrode within the cone be maintained and that the end of the electrode be uninfor ily spaced from the opening in the cone. An object of the present invention resides in. the provision of a method of assuring the desired uniformity of orientation of the electrode with respect to the open ended outer electrode. For convenience the conventional ate terminology will be used hereinafter in which the inner electrode is termed the keep-alive electrode or simply the. keep-alive and the outer-electrode that is usually conical in form is termed a gap electrode. The gap electrode conventionally is assembled opposite a similar (but solid) gap electrode in the device so as to impose the ionized discharge on the the case of attenuator tubes; and in the case of TR and ATR tubes, the gap electrodes produce breakdown at highlevel energy moments, in which case the keep-alive electrode furnishes a desired initial ionization level for fast responses to the high-level energy condition. The nature of the invention and its various features of novelty will be understood from the following detailed description of an'illustrative embodiment microwave transmission, in

thereof in contrast to acoured 10 in cone 24 and andbeading apparatus.

ventional prior art construction and procedure shown in the accompanying drawings. In the drawings:

Figures 1 to 3 illustrate, in fragmentary cross-sectional views, a typical prior art practice in the assembling of tubes of thisclass; and Figures 4 to 8 inclusive illustrate, in progressive stages, an improved procedure for assembling the keep-alive and gap electrode. Figure 9 shows a completed gap electrode and keep-alive assemlby together with a portion of the envelope of a gas tube to which the electrode assembly is to be inserted, and Figure 10 shows a complete TR tube containing the assembly of Figure 9. All of the views are enlarged.

Referring now to Figures 1 and 2, a center rod 10 of reduced cross-section at its lower end is sheathed or beaded with glass 12 in a preliminary operation; and also in a preliminary operation, collar 14 is sealed to ,a short length of glass tube 16. These are oriented in ing and partly because of the cumulative tolerances-in the dimensions of the various parts. Glass portions'12 and 16 are fused together by gas heat in a seal 22 asshown in Figure 2, as one complete sub-assembly.

Another sub-assembly is formed as shown in Figure -2 of a pair of gap electrodes 24 and26 in opposed walls 28 of a rectangular length of metal waveguidewhich also forms the envelope wall containing ionizable gas. As shown in Figure 2, the keep-alive sub-assembly is to beinserted concentrically within the hollow gap electrode 24. In an efiortto insure this result, a ring 30 is inserted care fully into a circular recess in wall 28 of the waveguide, after cone 24 is itself carefully centered in this recess, and both are brazed in place. When sleeve 14 is seated in ring 30 and soldered or brazed, the concentricity of the axial spacing of the lower to an illustrative embodiment of the present invention for avoiding such nonuniformity.

The accuracy required is of the order of- .001 inch.

cone mayv be no more than .040 inch. The cone angle in this assembly may be'18 degrees, measured between the axis and a straight-line element of the cone.

As shown in Figures 4 and 5, the first steps in preparation of the desired electrode assembly are first, the beading of the keep-alive rod 10 with a glass sheath 42, followed by heat sealing of a short glasstube 43 to form a glass button 44 on glass sheath 42, with the aid of fixtures The tip of rod 10 is shown termihating within bead 42, a

,collet 4 is in. axial alignment with collet 45 and the lower coll'et 48 has a recess 50 formed in the collet jaws. 52. is provided within the bore in collet located a predetermined distance from the Astop 48, accurately bottom of re cess 50. A shouldered collar or metal sleeve 54 is re a suitable heating device,

straightness of rod 1% is assured aid of an optical magnifier.

forming gas is passed through a passage I electrode 24 are assembled as a endwise spacing between the ano es u ccived within collet 48 and is centered thereby without allowing for any spacing or tolerance between the exterior of that sleeve and the interior of collet 48. By means of advantageously, a single r-f coil 55 concentrically about button 44 and collar 54, a seal is formed to unit collar 54 in assembly to beaded rod 19, rigidly and hermetically. in this operation one critical dimension is definitely established, namely, the spacing between the tip 19a of keep-alive electrode and the bottom 54a of collar 54.

It is desirable that tip lilo be centered within collar 54, within reasonable limits, and for this reason the by inspection at the outset and the axial alignment of tip 10a with respect to chuck 48 is checked occasionally by replacing collet 54 in chuck 48 with a dummy plug 56 as shown in Figure 6a, this plug having portion 56a that should be aligned with tip 10a of the keep-alive before assembly to collet 54.

Apparatus shown in Figure 7 is for assembling the keepalive to the cone in a separate operation, before either of these electrodes is assembled to the metal envelope or wave-guide. In this operation the accurate concentricity of the cone about the keep-alive is uniformly assured. Further, the rejection of defective assemblies is easily madepossible by visual inspection and at a stage of the manufacture where the electrode assembly is comparatively inexpensive. The fabrication of one gap electrode and the keep-alive as a separate assembly, later to be assembled opposite another gap electrode in the waveguide,

represents an important feature of this invention.

The accuracy of this positioning when made according to Figures 1 and 2, only after actually completing a tube. Inspection was by actual operation and by X-ray examination. In the event of inaccuracy the whole costly product then had to be discarded, or at best reclaimed in an expensive procedure.

A pin 62 having tip 62a is accurately opposed to the tip 10:: of the keep-alive, pin 62 being vertically reciprocable with an axially slidable collet 64. In the event of was heretofore known,

any eccentricity of pin 62 in relationship to keep-alive 10,

one or the other of these is carefully adjusted with the Pin 62 is next raised to a position of clearance. Thereafter, cone 24 is deposited on collar 54 and pin 62 is lowered carefully to contact with tip 10a, at the same time adjusting the cone laterally so as to receive the tip 62a. Concentricity of cone 64 about keep-alive 10 is consequently assured to a high degree of accuracy.

Shroud 66 is next lowered about the assembly of electrodes 10 and 24, limited in its descent by screw 67 and down pin 62 through opening 62b to flow about gap electrode 24.

Brazing heat is then developed by induction coil 68 to unite electrode 24 and sleeve 54. The accurate keep-alive and gap electrode assembly as shown in Figure 9 is complete upon cooling.

In the fabrication of the discharge gap structure, there remains only the sealing of collar 54 in the recess 54a in the waveguide body (Fig. 9), effected by soldering or brazing, and conventional adjustment of the opposed'gap electrode 26. This is accomplished with a threaded tool inserted into portion 26a, by manipulating the tool to force the cone into proper adjustment.

It will thus be seen that the keep-alive and the-hollow unit in a preparatory series of operations followed by a separate operation of uniting this assembly to the waveguide which constitutes a part of the envelope wall. The keep-alive electrode is oriented with respect to the hollow gap electrode 24 in two principal operations, the first of which (Fig. 6) establishes the tip of the keep-alive electrode and the end of the hollow gap electrode, and the second of which (Fig. 8) insures the concentricity of the two. This separation of the endwise and concentric dimensional characteristics is elfected, utilizing collar 54, so as to achieve economically and directly, and at an early stage in the manufacture, what previously was accomplished indirectly and at final stage of tube manufacture.

In Figure 10 a completed TR tube is shown incorporating the assembly of the hollow gap electrode and the keep-alive. In contrast to the assembly in Figure 1 where collar 14 and ring 30 are separate parts, the form in Fig. 10 involves unitary collar 54. The unitary collar represents an improvement in that the possibility of a leaky seal (between portions 14 and 30) is avoided and cumulative error due to tolerances of the parts is also eliminated. Mechanical inspection of the relationship between cone 24 and the tip 10a of the keep-alive electrode is greatly simplified. By inspecting the electrode assembly before it is inserted into the metal waveguide body, X-ray inspection becomes unnecessary. The loss involved in rejecting an entire assembly such as that in Figure 1 because of inaccurate cone and keep-alive assemblies is eliminated.

Proper electrical performances can be reliably expected from the electrode assembly in Fig. 10 when the tube is completed. "The tube when complete has windows 74 sealed across the ends of rectangular waveguide portion 70 and is filled with a mixture of an ionizable gas and a quenching gas at low pressure. In operation, a. glow discharge is established between the keep-alive and the hollow cone to speed the intense discharge between cone 24 and cone 26 when high intensity energy is impressed upon one of the Windows 74. Break-down reliably occurs between the cones which produces a change in the transmission characteristic of the waveguide and refleets the high intensity energy. During the low level signaling conditions, the waveguide transmits the signal into one of the windows and out of the other, and under such conditions in the TR tube described, the ionized gas in the region of the keep-alive produces a minimum of effect on the signal, that is, there is a minimum of interact'ion between the low level transmission and the keep-alive. Cones 76 which do not have a keep-alive electrode, also participate in the formation of an etlective break-down during high level energy conditions.

The foregoing illustrative description relates to a signilicant improvement in the construction of a costly type of tube and represents an important gain both in uniformity of product and in manufacturing efficiency. The broader aspects of the invention are applicable to other forms of tubes employing electrode assemblies of this character as mentioned above, and accordinglythe appended claim should be accorded that latitude of interpretation that is consistent with the spirit and scope of the invention.

What is claimed is:

The method of making a microwave transmissioncoutrol tube, including the steps of assembling a keepalive electrode concentrically within a hollow openended electrode and with predetermined spacing between an end of the keep-alive electrode and the open end of the hollow electrode, uniting a further gap electrode to the envelope of a tube, and uniting the assembly of the hollow electrode and the keep-alive electrode to the envelope of the discharge tube opposite the further electrode which with said hollow electrode defines a break-down discharge gap.

References Cited in the file of this patent UNITED STATES PATENTS 

